As the amount of communication traffic increases, the authorized spectrum of a 3GPP becomes insufficient to provide higher network capacity. In order to further improve the utilization rate of frequency spectrum resources, the 3GPP is discussing that how unlicensed spectrums can be used with the help of the authorized spectrum, such as 2.4 GHz and 5 GHz frequency bands. The unlicensed spectrums are mainly used in systems such as WI-FI, BLUETOOTH, radar, medical care uses, and the like.
In general, access technologies, designed for an authorized frequency range, such as Long Term Evolution (LTE), are not applicable to use in unlicensed frequency ranges. Access technologies, such as LTE, have very high requirements for spectrum efficiency and user experience optimization. However, a Carrier Aggregation (CA) function enables the LTE to be deployed in an unlicensed frequency range. The 3GPP provides a concept of LTE Assisted Access (LAA), which can use the unlicensed spectrum with the help of LTE authorized spectrums. The unauthorized frequency spectrum can have two working modes. One working mode is a Supplemental Downlink (SDL), that is, only a downlink transmission subframe is included. The other working mode is a Time Division Duplexing (TDD) mode, that is, both the downlink subframe and an uplink subframe are included. The SDL can only be used by means of CA. However, the TDD mode can be used not only by means of the CA technology, but also by Dual Connectivity (DC), and can also be used independently.
Compared with a WI-FI system, the LTE system in the unauthorized frequency range can provide higher spectrum efficiency and larger coverage. Data traffic can be seamlessly switched between the authorized frequency range and the unauthorized frequency range based on the same core network. For users, this means a better broadband experience, a higher speed, a better stability, and more mobility.
Existing access technologies on an unlicensed spectrum, such as WI-FI, have a weak anti-interference capability. In order to avoid interference, the WI-FI system is designed with many interference avoidance rules, such as Carrier Sense Multiple Access/Collision Detection (CSMA/CD) method. The basic principle of the CSMA/CD method is to monitor whether there are other access points (APs) or terminals on the periphery sending/receiving signaling or data before an AP of WI-FI or a terminal sends signaling or data. If there are other APs or terminals on the periphery are sending/receiving signaling or data, monitoring is continued until no sending/receiving of the signaling or data. Otherwise, if there are no other APs or terminals on the periphery which are sending/receiving signaling or data, a random number is generated as a waiting time. In the waiting time, if no signaling or data transmission is detected, the AP or the terminal may begin sending signaling or data after the waiting time is completed. The process is shown as in FIG. 1.
Good orthogonality in the LTE network means there is no need to consider whether or not there are other base stations or other users around which are transmitting data, in the base station and the uplink and downlink transmissions of the user. If the LTE is used in the unlicensed frequency band, there is no need to consider whether or not other devices are using the unlicensed frequency band. In such a situation, WI-FI equipment is subjected to great interference. As long as there is a service, the WI-FI device will transmit data. No monitoring rule exists. An idle state of the channel can be detected only after the transmission of the LTE service is completed. After that, data transmission can be carried out.
Therefore, when the LTE network uses the unlicensed frequency band, one of the most key points is to ensure that the LAA can coexist with the existing access technologies (such as WI-FI) on a fair-friendly basis. However, there is no Listen Before Talk (LBT) mechanism to avoid collisions in the conventional LTE system.
Specifically, as shown in FIG. 2, it is assumed that a repetition period of the LBT detection is 10 milliseconds (ms), and an LBT occupancy duration is 1 ms, that is, one sub-frame. If a channel idle state is detected within the first LBT period shown in FIG. 2, this indicates that the surrounding interference is small. Then, other sub-frames in this period can be occupied. If a channel busy state is detected within the second LBT period, this indicates that the surrounding interference is heavy. Then, other sub-frames cannot be occupied in the period.
In this case, measurements of Radio Resource Management (RRM), how to measure a reference signal reception power (RSRP) and the reference signal reception quality (RSRQ) for example is problematic.